LONDON (AP) — Having sprinted, jumped and thrown, and then having collected their medals, the athletes who compete in the Olympic Stadium next summer would be wise to do a Forrest Gump and keep on running.

Because just a few hundred yards (meters) south of the arena, little more than a javelin throw away from the 80,000 spectators, is a historical and technological marvel of London that no Olympic visitor should miss: a merrily sludging river of raw sewage.

About 1 million tons per day of the stuff, from hundreds of thousands of toilets and storm drains across North London, flowing right there in huge tunnels under your feet. Sniff the air — aahhh! — and, with the right wind, the eggy odor will make your nose crinkle.

Granted, the Northern Outfall Sewer isn't the most aesthetic of London's sights. But it is among the most fascinating. It was hurriedly but thoughtfully built with 318 million bricks after the "Great Stink" of 1858, when the sewage-polluted River Thames grew so putrid in hot weather as to make London unbearable.

In Parliament, the curtains were soaked with chemicals to try to ward off the noxious stench and there was even talk of it decamping from the capital entirely. A measure of the severity of the stink was the rapidity with which lawmakers acted to solve it. Engineer Joseph Bazalgette was quickly commissioned to build a sewage network that would help purify the Thames. He did such a good job that his system still forms the basis for London's sewers a century and a half later.

Thanks, in part, to the 2012 games, this stupendous feat of Victorian engineering and other landmarks that speak to London's rich history but which are off the tourist trail are now easier to explore and to see — if, as Olympic organizers hope, you travel by bike or on foot.

Which you should. Having meat-packed myself into sweaty London Underground trains that risk being even more crowded next summer and, now, having lately explored some of the newly renovated sections of London's ever-expanding network of cycle paths, I'd recommend two wheels everytime. And not merely for that feeling of wind through your hair.

A sorry truism of the Olympic Games and other sporting extravaganzas is that they are performances by extremely fit and healthy people for spectators who are often very unfit, unhealthy and overweight. Newham, home to the Olympic Park, and neighboring Barking have the lowest physical activity rates of any London boroughs, with only 14-15 percent of adults doing sport or strenuous exercise three times a week for at least 30 minutes each time.

London is hoping its Olympics help to change some of this. Organizers are encouraging spectators to walk and cycle to events by making it easier for them to do so. The idea is that people get the walking-cycling bug and keep it long after the Olympics have moved on. To be green, London wants all spectators to leave their cars at home. The vast majority will travel on London public transport, which carries 12 million travelers on a normal day but will be even busier at games-time. Olympic planners expect at least 4 percent will cycle and walk and are aiming for more, not least to ease strain on trains.

Walking and cycling paths leading to venues have been spruced up and connected up. There's a lovely one, for example, that runs the length of the west side of the Olympic Park, beside a very pleasant canal with ducks and houseboats. The path has a fresh gravel top and, at one point, dips under four massive metal pipes that form part of Bazalgette's sewer system. There's a plaque there with his name and the construction date: 1862-63.

Olympic organizers say more than 25 million pounds (€28 million;$40 million) has been spent upgrading cycling and walking routes to all venues.

You see far more of a city by bike. London's transport authority offers free cycle maps; I picked up a bunch at Euston station before I explored.

One canal path took me from the Olympic Park south to Limehouse Basin on the Thames in 30 minutes of easy riding. From there, it was another absorbing cycle along quaint and mostly empty backstreets to the Tower of London that was thick with tourists.

The cycle maps show that, aside from occasional breaks here and there where cyclists would need to travel on roads, another path along Grand Union Canal, then Regent's Canal and finally Hertford Union Canal to the Olympic Park snakes right across North London. I rode the last few miles (kilometers) of this picturesque route, past brick houses with lush lawns abutting the canal.

The city's cycle hire scheme is also being expanded from central London eastward closer to the Olympic Park. Anyone aged 14 and over and with the right brand of credit card (not all cards are accepted) can take one of the 6,000 bicycles from any of 400 hire points.

They could be a smart way to explore Hyde Park that will host triathlon and marathon swimming next summer. There also are hire points around Lord's Cricket Ground that will host archery and Horse Guards Parade where there'll be beach volleyball. The bikes could also suit Londoners or any visitor simply trying to move around the Olympic-congested city.

"By 2012, we'll be able to invite the entire world to join London's cycling revolution," Mayor Boris Johnson declared last November.

Organizers say cyclists won't be allowed to take bikes into the Olympic Park but there will be free and secure parking at all venues.

Lobbying groups welcome London's cycling and walking improvements but would like even more and say the city still lags behind cycle-friendly Amsterdam or Copenhagen. But cyclists also say the city is much safer to ride around than it used to be and that the 2005 terror attacks on public transport and London's tax on vehicles that drive in the city center have prompted more people to ride bikes.

In its own modest way, the Olympics could help that trend. Watching Olympic sport and getting fitter at the same time: how's that for an idea?

"This our chance to sort out some of the lazy cultures we've got into," says the appropriately named Jim Walker, who chairs a group advising Olympic organizers how to encourage more "active travel" at games-time.

"It will be an opportunity for us to get it right for 16 days and, as a legacy for London, to flow much better afterward."